The electrolysis of aqueous solutions of ionizable chemical compounds in a cell equipped with an anode and a cathode is well known to the art. One of the most commercially significant applications is the production of halogens particularly chlorine and alkali metal hydroxides, particularly sodium and potassium hydroxide by the electrolysis of aqueous alkali metal halide solutions. A type of electrolytic cell utilized in the commercial manufacture of such materials is a diaphragm-type cell. The configuration and operation of these cells is well-known to the art and while the design of the cell may vary from one manufacturer to another, broadly they consist of three basic elements: the anode base element, the cathode can element and the cover. In some cases, the anodes may extend from the top or the sides of the cell rather than extending from the bottom, and in those cases, the said top or side becomes the base for the purposes contemplated herein. But, the general configuration or relationship between the component parts remains the same. Attached to and forming a part of the cathode structure will be a diaphragm or percolating separator. A diaphragm as used in this application may also encompass membranes, microporous separators and other types of percolating or ion exchange separators used in various electrolytic cells.
Although approximately 50% of chlorine and caustic commercially produced in the world today results from a diaphragm type electrolytic cell, a number of problems are inherent in the cells limiting their application, and imposing limitations upon the degree of efficiency with which the existing cells may be operated. For example, most commercial cells today are operated with a discrete gap between electrodes. Gap as used in this application is defined as the distance between the anodic active surface of the anode and the surface of the diaphragm or separator exposed to the anode. This gap is filled with the electrolyte, and the resistance of the electrolyte to the passage of electrical current is significant. Quantities of energy are wasted, serving only to raise the temperature of the electrolyte, and ultimately, limiting the current density at which the cell may be operated. Although the gap is effective in producing quantities of the desired materials, efficiency can be increased by placing the electrodes more closely together in order to reduce the current losses. The difficulties in reducing the electrode gap are great due to a number of factors. Cathodes are generally foraminous mesh screens which become distorted, misshapen, and bent through use and with age. In addition, the diaphragm material is generally deposited upon the surface of the cathode in a particulate slurry deposition operation; and normally produces a diaphragm of non-uniform thickness. Therefore, the difficulty in controlling the gap size is increased. The introduction into the electrolysis art of dimensionally stable anodes has likewise created problems in the positioning of the anodes to give the desired gap between anode and cathode. These dimensionally stable anodes comprise an electrocatalytic active coating, for example, platinum or precious metal oxide or mixtures thereof, on an electrically conductive substrate, generally a valve metal such as titanium. The construction of these anodes out of valve metals and application of the electroactive coating, has resulted in a structure which is more precise and longer lasting than the graphite anodes which they are replacing, but being a manufactured product, the tolerances of manufacture still allow for material deviations which may cause problems in electrode gap alignment.
In order to minimize alignment problems and to increase the ease of installation, many types of electrodes configurations have been employed. One such configuration is described in U.S. Pat. No. 3,674,676 to Fogelman, in which is described a dimensionally stable anode which is expanded after insertion into the cell in order to reduce the anode/cathode gap. Fogelman employs electrically conductive connectors for expanding his anodes and requires in all embodiments the use of a single riser post. U.S. Pat. No. 3,803,016 to Connor describes an anode assembly which is adjustable to allow for the precise determination of the anode to the cathode gap. U.S. Pat. No. 3,941,676 to Macken discloses an adjustable electrode in which the electrode surfaces are expanded through a cam-type arrangement. U.S. Pat. No. 3,796,648 to Connor et al. likewise discloses a method of adjusting the electrode gaps through a modification of the base plate which supports the anodes in the cell. It is obvious from the above prior art that attention has been directed to the adaptation of the anode base and techniques for the modification of the attachment of the anodes to the said base through movable/adjustable riser posts. Also, considerable attention has been given to methods for expanding the anode plate surfaces after they are installed within the cell.
It is the object of this present invention to provide a means for reducing and controlling the gap or space between electrodes in an electrolysis cell, by compressing the electrodes during installation and allowing a resilient, compressible, element within each electrode assembly to continually force both faces to a predetermined location which will determine the gap between adjacent electrodes.
Another objective of this invention is to provide a simple method of installing electrodes within a cell with a minimum of labor and establishing precise electrode-electrode gaps automatically.